Augmenting solute clearance in peritoneal dialysis (original) (raw)
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A quantitative description of solute and fluid transport during peritoneal dialysis
Kidney International, 1992
To investigate the relationship between dialysate glucose concentration and peritoneal fluid and solute transport parameters, 41 six-hour single dwell studies with standard glucose-based dialysis fluids containing 1.36% (N = 9), 2.27% (N = 9) and 3.86% (N = 23) anhydrous glucose were carried out in 33 clinically-stable continuous ambulatory peritoneal dialysis (CAPD) patients. Intraperitoneal dialysate volumes (VD) were determined from the dilution of 131I-albumin with a correction applied for its elimination from the peritoneal cavity (KE, ml/min). Diffusive mass transport coefficients (KBD) were calculated from aqueous solute concentrations (with a correction applied for the plasma protein concentration and, for electrolytes, also for the Donnan factor) during a period of dialysate isovolemia. The intraperitoneal amount calculated to be transported by diffusion was subtracted from the measured total amount of solutes in the dialysate, yielding an estimate of non-diffusive solute transport. The intraperitoneal dialysate volume over time curve was characterized by: initial net ultrafiltration (lasting on average 92 min, 160 min and 197 min and with maximum mean net ultrafiltration rates 6 ml/min, 8 ml/min and 14 ml/min, respectively, for the 1.36%, 2.27% and 3.86% solutions); dialysate isovolemia (lasting about 120 min for all three solutions) and fluid reabsorption (rate about 1 ml/min for all three solutions). KBD for glucose, potassium, creatinine, urea and total protein did not differ between the three solutions and the fractional absorption of glucose was almost identical for the three glucose solutions, indicating that the diffusive transport properties of the peritoneum is not influenced by the initial concentration of glucose or the ultrafiltration flow rate. About 50% of the total absorption of glucose occurred during the first 90 minutes of the dwell. The mean percentage of the initial amount of glucose which had been absorbed (%GA) at time t during the dwell could be described (r = 0.999) for all three solutions using the experimental formula %GA = 85 - 75.7 * e-0.005*t. After 360 minutes, about 75% of the initial intraperitoneal glucose amount had been absorbed corresponding to a mean (+/- SD) energy supply of 75 +/- 6 kcal, 131 +/- 18 kcal and 211 +/- 26 kcal for the three solutions. Non-diffusive (that is, mainly convective) transport was almost negligible for the less hypertonic solutions while it was estimated to account for 30 to 40% of the total peritoneal transport of urea, creatinine and potassium during the first 60 minutes of the 3.86% exchange.
Peritoneal Dialysis International, 2016
♦ Background: Peritoneal dialysis (PD) has limited power for liquid extraction (ultrafiltration), so fluid overload remains a major cause of treatment failure. ♦ Methods: We present steady concentration peritonal dialysis (SCPD), which increases ultrafiltration of PD exchanges by maintaining a constant peritoneal glucose concentration. This is achieved by infusing 50% glucose solution at a constant rate (typically 40 mL/h) during the 4-hour dwell of a 2-L 1.36% glucose exchange. We treated 21 fluid overload episodes on 6 PD patients with high or average-high peritoneal transport characteristics who refused hemodialysis as an alternative. Each treatment consisted of a single session with 1 to 4 SCPD exchanges (as needed). ♦ Results: Ultrafiltration averaged 653 ± 363 mL/4 h — twice the ultrafiltration of the peritoneal equilibration test (PET) (300 ± 251 mL/4 h, p < 0.001) and 6-fold the daily ultrafiltration (100 ± 123 mL/4 h, p < 0.001). Serum and peritoneal glucose stability...
Ultrafiltration and solute kinetics using low sodium peritoneal dialysate
Kidney International, 1995
Low sodium peritoneal dialysate has been reported to enhance sodium loss and alleviate signs of fluid overload in continuous ambulatory peritoneal dialysis patients. To elucidate the mechanisms involved, we compared ultrafiltration and solute kinetics using low sodium dialysate (LNaD; 105 mEq/liter sodium, 2.5% glucose, 348 mOsm/liter), conventional dialysate with equal osmolality (CD1.5; 132 mEq/liter sodium, 1.5% glucose, 348 mOsm/liter) and conventional dialysate with equal glucose concentration (CD2.5; 132 mEq/liter sodium, 2.5% glucose, 403 mOsm/liter). A 2 liter, six hour exchange of each dialysate was performed on separate days in 10 chronic peritoneal dialysis patients. Transperitoneal solute diffusion was assessed by calculating the permeability-area product (PA) of the peritoneal membrane from the dependence of plasma and dialysate solute concentrations on tie. Net fluid removed using LNaD of 190 +/- 90 (SEM) ml was similar to that using CD2.5 (250 +/- 90 ml) but higher (P < 0.01) than that using CD1.5 (-200 +/- 60 ml). Sodium loss was higher using LNaD (72 +/- 11 mEq, P < 0.01) and CD2.5 (41 +/- 12 mEq, P < 0.05) than using CD1.5 (-18 +/- 8 mEq). Changes in plasma sodium concentration were small during each dwell and were not different among the study dialysates. PA values for urea (23.4 +/- 1.6 ml/min), creatinine (10.0 +/- 1.0 ml/min), and glucose (10.3 +/- 1.3 ml/min) were similar when determined in each dialysate. The PA value for sodium (7.6 +/- 1.5 ml/min) could only be accurately determined in LNaD. We conclude that: (1) net fluid removed is greater using LNaD than CD1.5 despite similar osmolalities because LNaD has a higher glucose concentration and glucose is a more effective osmotic solute than sodium; (2) sodium loss when using LNaD is enhanced by both diffusion and convection; and (3) sodium diffuses across the peritoneum slower than urea, creatinine and glucose. These data suggest that LNaD alleviates signs of fluid overload by increasing net fluid removal and enhancing sodium loss.
American Journal of Kidney Diseases, 2005
Background: Residual renal function (RRF) contributes substantially to the adequacy of peritoneal dialysis (PD). In the presence of RRF, maintenance of an adequate fluid balance is facilitated, level of systemic inflammation is lower, and renal endocrine functions are preserved. The beneficial impact of RRF also may be related to the preservation of specific renal elimination mechanisms, such as tubular metabolism or secretion, which are crucial for the removal of some uremic retention solutes. Methods: Time profiles of peritoneal and renal clearances of urea nitrogen (60 d), creatinine (113 d), phosphate (96 d), the middle molecule  2-microglobulin ( 2 M; 11.8 kd), and the protein-bound solute p-cresol (108 d) were investigated prospectively in 24 incident PD patients. Data were analyzed by using the linear mixed models procedure. Results: During a median follow-up of 7.2 months (range, 5.6 to 8.6 months), RRF (P ؍ 0.001) and 24-hour urine volume (P ؍ 0.004) declined significantly. Twenty-four-hour peritoneal drainage volume increased (P < 0.0001). Renal clearances of urea nitrogen (P ؍ 0.0002), creatinine (P ؍ 0.001), and phosphate (P ؍ 0.001) decreased. Peritoneal clearances of these solutes increased (P ؍ 0.002, P < 0.0001, and P < 0.0001, respectively). There was a decline in renal clearances of  2 M (P ؍ 0.0004) and p-cresol (P < 0.0001). No change in peritoneal clearances of these solutes was noted (P ؍ 0.188 and P ؍ 0.559, respectively). Conclusion: Increasing PD dose may compensate for deteriorating RRF with respect to the elimination of water-soluble solutes. This is not the case for the middle molecule  2 M and the protein-bound solute p-cresol. Am J Kidney Dis 46:512-519.
Kidney International, 2004
Longitudinal relationship between solute transport and ultrafiltration capacity in peritoneal dialysis patients. Background. Time on treatment is associated with a greater risk of impaired ultrafiltration (UF) in peritoneal dialysis (PD) patients. In addition to increasing solute transport, a potentially treatable cause of impaired ultrafiltration, cross-sectional studies suggest that there is also reduced osmotic conductance of the membrane. If this were the case then it would be expected that the UF capacity for a given rate of solute transport would change with time. The purpose of this analysis was to establish how solute transport and UF capacity change relative to one another with time on therapy. Methods. Membrane function, using a standard peritoneal equilibration test, was measured at least annually in a wellcharacterized, single-center observational cohort of PD patients between 1990 and 2003. Demography included age, gender, original cause of renal failure, body surface area (BSA), validated comorbidity score, residual urine volume and urea clearances, peritoneal urea clearances, and plasma albumin. Results. Data from 574 new PD patients were available for analysis. Independent demographic factors associated with higher solute transport at baseline were male gender and higher residual urine volume. Throughout time on therapy there was a negative relationship between solute transport and UF capacity and a significant increase and decrease in these parameters, respectively. During the first 12 months of treatment, the increase in solute transport was not associated with the expected fall in UF capacity, a phenomenon that was not explained by informative censoring, but was associated with an increased, albeit weak, correlation with BSA. In contrast, later in treatment there was a disproportionate fall in UF capacity, more accelerated in patients developing UF failure. Early exposure to higher intraperitoneal glucose concentrations, in the context of more comorbidity and relative lack of residual renal function, was associated with more rapid deterioration in membrane function. Conclusion. Despite a causal link between solute transport and UF capacity of the membrane, due to the effect of the former on the osmotic gradient, there is evidence of their longitudinal dissociation. This implies a change in the structure-function
Effect of increased dialysate fill volume on peritoneal fluid and solute transport
Kidney International, 1997
It has recently been recommended that the peritoneal dialysate volume should in general be increased to increase the peritoneal small solute clearances. However, the net ultrafiltration volume may decrease due to higher intraperitoneal hydrostatic pressure (IPP) and higher peritoneal fluid absorption induced by higher fill volume. In the present study, we investigated the effects of increasing the fill volume on peritoneal fluid and solute transport. A four-hour dwell study with frequent dialysate and blood sampling was performed in 32 male Sprague-Dawley rats using 16 ml, 25 ml, 30 ml or 40 ml (8 rats in each group) of 3.86% glucose solution with 131I albumin as an intraperitoneal volume marker. The peritoneal transport of fluid, glucose, urea, sodium, potassium, phosphate and total protein as well as IPP with different fill volume were evaluated. The IPP and peritoneal fluid absorption rate (as estimated from the 131I albumin elimination coefficient, KE) significantly increased with increase in fill volume (P < 0.05), whereas the direct lymphatic absorption did not change with increasing fill volume. There was a strong correlation between IPP and KE. However, the net ultrafiltration volume was significantly higher in the high fill volume groups compared to the low fill volume groups, mainly due to a better maintenance of the dialysate to plasma glucose concentration gradient in the high fill volume groups. There was no significant difference in the diffusive mass transport coefficients (KBD) and sieving coefficients for any of the investigated solutes, although KBD values tended to be lower in the 16 ml group. The clearances for small solutes increased with increased fill volume, although these increases were slightly smaller than predicted from the increase in fill volume. We conclude that: (1) An increase in dialysate fill volume using 3.86% glucose solution results in higher intraperitoneal hydrostatic pressure and higher peritoneal fluid absorption, but, on the other hand, a higher net ultrafiltration; (2) The increase in net ultrafiltration with increased fill volume is mainly due to a better maintenance of glucose concentration in the dialysate, inducing an increased transcapillary ultrafiltration rate; (3) Solute clearances increase although not quite to the same extent as predicted from the increase in fill volume. Our results indicate that decreased net ultrafiltration volume associated with higher dialysate fill volume (due to higher IPP and higher peritoneal fluid absorption) could be avoided if hypertonic glucose solutions are used.
Peritoneal Fluid and Solute Transport
Journal of the American Society of Nephrology, 2002
ABSTRACT. The integrity of the peritoneal membrane in peritoneal dialysis (PD) is of major importance for adequate dialysis and fluid balance. However, alterations in peritoneal fluid transport, such as ultrafiltration failure, often develop during long-term PD. To investigate peritoneal solute and fluid transport and to analyze the influence of treatment time, peritonitis incidence, and PD modality (continuous ambulatory PD [CAPD] or automated PD [APD]), a cross-sectional study with an extended peritoneal transport test that used dextran 70 in 2 L of glucose was performed in 23 nonselected chronic PD patients. Compared were long-term (>40 mo) with short-term PD patients (<40 mo), CAPD with APD patients, and those with a peritonitis incidence of >0.25/yr to those with an incidence of <0.25/yr. Dialysate/plasma (D/P) ratio and mass transfer area coefficient of creatinine, lymphatic absorption rate (LAR), transcapillary ultrafiltration, and effective ultrafiltration were m...
The Prescription of Peritoneal Dialysis
Seminars in Dialysis, 2008
In addition to the maintenance of normal extracellular electrolyte composition, the prescription of continuous peritoneal dialysis (CPD) should address four other specific issues: (i) prevention of uremia by achievement of adequate clearance of azotemic substances, (ii) prevention of progressive expansion of the extracellular volume by adequate peritoneal ultrafiltration, (iii) prevention of loss of residual renal function, and (iv) prevention of deterioration of the peritoneal membrane structure and function. Urea clearance, in the form of Kt/VUrea, is the index of removal of azotemic substances proposed by current guidelines. The target total (renal plus peritoneal) Kt/VUrea is ≥1.7 weekly. To provide the desired peritoneal Kt/VUrea (Kpt/VUrea), the prescription of peritoneal dialysis must provide a daily drain volume (Dv) defined by the clearance equations as Dv = V × (Kpt/VUrea)/(D/PUrea), where V is body water obtained from published anthropometric formulas, Kpt/VUrea = (1.7 − renal Kt/VUrea)/7 and D/PUrea is the dialysate-to-plasma urea concentration ratio at the dwell time prescribed. Computer programs obtain the relevant D/PUrea values from formal studies of peritoneal transport. In the absence of these studies (for example, at initiation of CPD), D/PUrea values can be obtained from published studies with similar dwell times. Body size, indicated by V, is the major determinant of the Kpt/VUrea limit provided by a given CPD schedule. Other obstacles to achievement of adequate urea clearance are created by poor patient compliance, inaccuracies of the anthropometric formulas estimating V, and mechanical complications of CPD that lead to retention of dialysate in the body. The main requirements for the prescription of adequate ultrafiltration are knowledge of the individual peritoneal transport characteristics, monitoring of urinary volume, and restriction of dietary sodium intake. Excessive dietary sodium intake is the major cause of extracellular volume expansion in CPD. Ideally, sodium intake should be kept at the level of total (peritoneal plus renal) sodium removal. Preventing the loss of residual renal function involves avoidance of nephrotoxic influences in the form of medications, radiocontrast agents, urinary obstruction and infection, and possibly other influences, such an elevated calcium–phosphorus product and anemia. Use of the lowest dialysate dextrose concentration that will allow adequate ultrafiltration is currently the most widespread practical measure of prevention of peritoneal membrane deterioration. Formulation of biocompatible dialysate is a major ongoing research effort and may greatly enhance the success of CPD in the future.